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OI-codes/Luogu/P3607/P3607.cpp

58 lines
1.4 KiB
C++

#include <iostream>
#include <algorithm>
using std::cin;
using std::cout;
const char endl = '\n';
const int N = 55;
int n, a[N], f[N][N][N][N];
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> a[i];
}
for (int l = 1; l <= n; l++) {
for (int i = 1; i <= a[l]; i++) {
for (int j = a[l]; j <= 50; j++) {
f[l][l][i][j] = 1;
}
}
}
for (int len = 2; len <= n; len++) {
for (int l = 1, r = len; r <= n; l++, r++) {
for (int i = 1; i <= 50; i++) {
for (int j = i; j <= 50; j++) {
f[l][r][i][j] = std::max({
f[l][r][i][j],
f[l + 1][r][i][j] + (a[l] == i),
f[l][r - 1][i][j] + (a[r] == j),
f[l + 1][r - 1][i][j] + (a[r] == i) + (a[l] == j),
});
f[l][r][i][j + 1] = std::max(f[l][r][i][j + 1], f[l][r][i][j]);
f[l][r][i - 1][j] = std::max(f[l][r][i - 1][j], f[l][r][i][j]);
}
}
for (int j = 1; j <= 50; j++) {
for (int i = j; i; i--) {
f[l][r][i - 1][j] = std::max(f[l][r][i - 1][j], f[l][r][i][j]);
}
}
}
}
cout << f[1][n][1][50] << endl;
return 0;
}